Gate valve



Jan. 9, 1951 p, LAURENT 2,537,470

' GATE VALVE Filed June 29, 1948 4 Sheets-Sheet l gwvQ/WM /7 Mali-m1 BLaurenZ Jan. 9, 1951 'M. P. LAURENT GATE VALVE 4 Sheets-Sheet 4 Filed June 29, 1948 gwuwwbom MiiZfinRLaarenZ Patented Jan. 9, 1951 ICE VADVE.

Milton iBaul Lament, Houston, fliex iassignor to W-K-nM @Gompany, 5a ;par.tners'hip Application 'J'une29, 1948,,Seria1.No..35,857

This invention rt-ila tes to a through conduit" type 'of sliding-gate valve. By' the t'erm-through conduit is meant a valve which, in its openposition,- 1eaves the conduit (entirely unobstructed to flow at the valve opening. Such gate valves usually 'are employed to control the flow in conduits carrying qarge volumes =of fluids, such as or oil. The through conduit gate 'valve provided by this invention effectively controls the i-low =of fluids which may be at high temperature, high ran-assure, andfor of arcorrosive nature. Z'My =proved va'lve :serves under such difiicu'lt con'die tions -'not-only'withou t leakage, but also without undue *wear of the sealing surfaces of the valve, thereby adding greatly to its service life.

Gate valves intended for use "under these conditions frequently are provided 'With a ported gateef sectional or multi par t construction. The sectional valve gate has relatively movable sealing elements which are mechanically forced apart to seat oppositely against the valve seats that surround the ports in the valve housing. This expansion of the gate e'fiec'ts a tight :seal btween the gate and the valve seats when the valve is in either open or closed position.

In valves of Ik-nown construction, the mechanical i'orces, which seat the gate e'lements, usually are provided -by n 'wedging action 'ihe'tween the separate sections of the gate. Such a wedg ing action takes place during 'the "final movement of the ='gate,'-propel1ed by a conventional valve stem, into fully open or fully=closed :position. 'Tozunseat the gate sealing elements and permit the gate "to be moved easily and freely ihetwz-ren =open and closed positions :of the "valve, springs usually :are employed to contract the gate. Such springs :are efieotiue to contract the gate after the expanding forces have been relieved, 51. :e. after initial movement of the gate from the fully open or fully closed position. Contracting spr ings, however, are subject to breakage, are not necessarily :posittive in their action, and complicate the gate construction. In :addition, tspr ing contraction is not (controllable to adjust the clearance Zhetween the gate sealing elements and -their-seats. Such controlled contraction :and thereby clearance, :is desirable in "order to prevent excessive escape of lubricant irom the valve housing into the ill-HE tor rcon'duit.

Contraction of the gate, upon relief 0f the expansive or :seating iorces, also is necessary to avoid .a practical condition, known as pressure .lock. 'Thus,.if the 'valve is \closed andzsealed and the :fiuid pressure within the valve housing :is greater than the pressure on both :sides of line, the gate sealing-=el'e1nentssale hydraulicallly held against their seats. Under this :condition, if no means are *provided to positively contract the gate elements, when the mechanical expansive *forces :are reh'eved, -the hydraulic :seati-ng forces tend to bind or wedge, so to speak, the entire gate against movement. Su'ch a :bound state, known as pressure )lock, often renders movement of the gate from closed to open position-difficu lt to initiate. 1

Expansion of the gate during its tfinal movement into op em or clo's ed position i i-s =ob j'ectionabl e, because such action results in a Wiping or dragging efiect between the sealing surfaces off the valve. A Wiping action between thessealing surfaces of ithe gate elements and the naive :seats, while such surfaces are in loaded :con'tact, .e.

forcefully :pr'essed together, :causes :rap'id wear and sometimes ,galling of these accurately m-achined and highly polished surfaces. Leakageiis the iconseduent :result. Furthermore, :sealing :surfaces that undergo 'such wiping action must :be formed of materials which resist :the attendant wear. isuchunateriails arenotralways those which aprovrideaneffectivesealing surface or those which bes't endure :seating stresses without iracture.

Accordingly, it is .an object oi this invention to iprovide a gate -lza'lre having a sectional gate in the :moua'lo'le vagate elements :seat and unseat, normally :of the valve rseats, after :the :gate has reached :tully open :or itully closed position. .Hence, twi'ping .action between loaded :sea'ling :surfaces of ithe'izalve is entirelyfavoi'ded. The avoid :ance of such wiping (action not only eliminates :a'ibrasive wvear of the sealing surfaces, .but also enables :a much wider choice -:of materials ior construction.

.hn'othericbiect of this invention is to .provideza gate (or the type under consideration in which contraction of the gate .is accomplished 'aviiihoutxtheiuseiof springs.

Apfurther object :of thiszinventionis to provide a ;gate valve having .:a sectional gate thatmay he positively expanded or contracted, independently of the cperation-of zthe'valve stem.

:Still another toojectzof this invention is to provide a gate valve of the type under -consider-ation :in which contraction .of the gateis controllable to adjust amount -.of clearance between the ;gate sealing elements :and theinseats.

Still azuoither :obieot of this invention is to prowlide a gate walve having .a sectional gate that provided "with means ;.for :positively overcoming the :adverse .efiects :of a pressure :lock condition.

A turther object ot thi invention ;is the provide a gate valve of sturdy construction which is especially adapted for long service and reliable under high pressure, high temperature, and/or corrosive conditions.

Other ob ects and advantages of the invention will be apparent from the following description and accompanying drawings in which:

Figure 1 is a vertical View, partly in section, of a gate valve, of the rising stem type, embodying this invention. The valve is shown in open position and with the gate elements expanded into sealing engagement with the valve seats.

Figure 2 is a fragmentary view, partly in section, taken partially on a line corresponding to 22 of Figure l, but showing the valve in closed position, and with the gate elements unseated from the valve seats.

Figure 3 is a fragmentary sectional View taken on line 33 of Figure 1.

Figure 4 is a fragmentary sectional View corresponding to Figure 3, but showing the gate elements unseated from the valve seats.

Figure 5 is an exploded perspective view of the component parts of the valve gate, and a portion of the valve stem embodying this invention.

Figure 6 is a fragmentary sectional view corresponding to Figure 3 showing a modification of the invention. 7

Figure 7 is an elevational view, partly in section, of a modified form of the center section of the gatefor use in a valve of the non-rising stem type.

Figure 8 is a perspective view of the bushing shown in Figure 7.

Referring now to the drawings, Figures 1 and 2 show a through conduit gate valve, of the rising stem type, having a housing l0 provided with an interior chamber 1 in which is housed the gate mechanism of the valve. Aligned ports i2 and it, formed in opposite walls of the housing 10, are provided with parallel, preferably removable, opposed valve seats {4, which may contain conventional sealing rings 15. The valve seats i4 have side flanges or guides it which, together with the seats it, serve to guide and confine the gate-to substantially rectilinear movement for opening and closing the valve. The chamber ii is closed at its lower. end by a closure plate ll which is secured in place by an annular retaining member it. A wedge-shaped sealing gasket I9 is interposed between the periphery of the plate I! and the mouth of the chamber H to provide a pressure-responsive seal. A valve stem 2i having threaded engagement with a conventional hand- I wheel 2i extends through a packing gland 22 at the upper end of the chamber H. The stem 28 is non-rotatably connected to the gate, so that rotation of the handwheel 2i raises and lowers the stem 28 to thereby open and close the valve. A conventional pressure lubrication fitting Ha is threaded into the closure plate I! inorder to supply the chamber II with lubricant, usually grease, as is customary in valves of this type. The structure thus far described is known and, accordingly, no further detailed description is believed necessary.

The ported valve gate assembly which slides between the valve seats 14 in the guides 16 is formed in three sections, two outer segments 23, and an intermediate core 24, as best shown in Figure 5. The core and the segments have ports 25 and 26, respectively, which in the open position of the gate assembly, as shown in Figure 1, are aligned with the housing ports l2 and L3 to permit unobstructed passage of fluid through the valve. lhe core also may be cored out, as indicated at 2511, for weight reduction.

The gate when assembled is substantially rectangular in horizontal section, as shown in Figures 3 and 4, so that the flat parallel outer faces 2'! of the segments 23 may sealingly engage the corresponding flat faced valve seats 14. It will be understood, however, that the sealing faces of the segments and the seats may be arcuate, or other suitable shape, in horizontal section. Such other shapes are possible of use, provided the correspending sealing surfaces extend parallel to the direction of travel (i. e. endwise movement) of the gate. This surface orientation will permit movement of the gate between open and closed positions yet provide the desired sealing surfaces.

The inner faces 28 of the segments 23 diverge laterally of the gate, as best shown in Figures 3 and 4. The core 26 also has laterally divergent faces 29 each of which extends parallel to a corresponding face 28 of the segments. Hence, lateral displacement of the core 24 relative to the segments 23 in one direction (to the left in Figures 3 and 4) results in a mutual wedging action between the two sets of inner abutting faces 28 and 29 of the gate sections. This wedging action is effective to expand the gate normally of the valve seats 64. Such expansion is sufilcient to force the outer faces 21 of the two segments 23 into tight sealing engagement with their respective valve seats i l. During expansion of the gate, the segments 23 are held against lateral displacement by the guides IB, so that the segments are forced to move and seat normally against the valve seats l4. Hence, no wiping action occurs between the seat and segment sealing surfaces, while such surfaces are being placed under the seating load. It also will be understood that, although the wedging surfaces of the core and segments are shown as fiat, these surfaces maybe of other suitable configuration, such as arcuate, in vertical section. Such other shapes are possible of use provided the opposed surfaces of each set are laterally parallel and the two sets of such surfaces are laterally divergent. This surface orientation will permit lateral dislacement of the core yet retain the desired wedging effect.

Bothends, i. e. the top and bottom, of each segment 23 are connected to the core 24 by a lip or rib 30 which fits into a corresponding groove 31 in, an overlapping portion of the core, as best shown in Figure 1. The interfitting lip 30, and groove 3| of each connection extend parallel to the corresponding set of abutting faces 28 and 29 of the core and segments. Hence, the cooperating side faces 32 and 33 of the lips and the grooves, respectively, form wedging surfaces which are opposite in operative effect to the previously mentioned wedging surfaces. Accordingly, lateral displacement of the core 24 (to the right in Figures 3 and 4) is effective to contract the gate and pull the outer face 2! of at least one of the two segments 23 out of sealing engagement with its valve seat M. It is obvious that other types of equivalent mechanical connections may provide the desired contracting effect. For example, dovetailed ribs and grooves (not shown) may directly connect the abutting faces of the segments and the core intermediate their ends.

Lateral displacement of the core 24 is accomplished by means of the -T-head and under-cut groove structure, shown best in Figures 2 and 5. A lateral edge of the core has an endwise-extending groove 34 which is provided with overhangseats 14.

asse -eve :ingwalls 35,'=at both end portions thereof. IQne end of a lateral stub shazfit 3t :has ism enlarged :square :or rectangular :head 31, fits "the :groove til :ior relative :s'lid'eabl'e "movement therein .in') open or closed position, the overhanging wall portions 3.5 preventrwithdrawal and? the :31 out of the groove 34 :so that ilateral of the :shaft in either direction, :efl'ects displacement of the ecore r-relative :tothe segments. The other end of the shaft :36 threadedly iresolved :in a thimble latter is journalled in :a side wall portion of the housing t1] is provided with .an operating handle .3 9. .Axialladisplacement of the thimble 3.8 is prevented by an annular enlargement 4353 which its 'aicorresponding annular recess 4;! tin =zthe2hou-sing wall. :movable closure plate &2, which :iorms :one :side wall :of the recess a4sl, permits insertion of the .thimble .into place. Suitable paele'ng :hetween the enlargement 4B and the walls of the annular ireoess 41 prevents leakage through the wvailof the housinglfi. if .desired, :a grease conduit 43 open into the recess 24. L, ;in order to the able to :introduce :a suitable lubricant :to the :packing.

Because of the non-rotatable connection between the head .31 .and the :groove 3.4, :rotation of the thim'ble 3.8, .by the :handle 53.9, positively moves the shaft 3 6 axially in either direction and laterally of the gate. The connection between the shaft 36 and the core :24 :is such that the core may be displaced laterally .by the shaft,

whenever the gate is in (or mearly in) open :or closed position. This connection, however, :permits :thecore tomove transversely of the shaft during end-wise movement of :the gate, ibetween open and closed positions f the valve. Hence, turning the handle 39 is effective to positively expand or contract the gate to :seal or unseal the valve. The amount of lateral displacement of thezcore necessary to @expand or'contractthei'gate the required amount is relatively small. Ac-

cordingly, the pitch of the threads connecting the shaft 36 to the thimble 3.8 may Ebe so .pro- ,portioned that only a quarter turn 'of the thimble is necessary to seal or unseal the valve. It will be [noted that contraction of the gate by the handle 39 is controllable .to limit theiamount of clearance between the segments 523 and their Hence, excessive escape of rlubricant from the chamber 1:! into the how time unay :be ,prevented.

The gate is raised and lowered, that is, moved between open and closed positions, 'byithe valve .stem 20 which is connected to :the :core .24 -:by B. T-head :and slot construction. The lower .end of the stem is provided with an enlarged head 44 which fits .into an undercut .slot :45 'in :one end of the core, thus preventing turning of the stem 20 upon rotation of the-"handwh'eel 2 L .Sui-

ficient clearance is provided between (the :stem' 20 and head 44 and the lateral :sides :of the slot 45 for lateral displacement :of the 200118 224 with respect to the :stem 2.0 during expansion and contraction of the gate. islot45, as shown .inFigure 5,-opens :to one sideface 29.01 the core in order to permit'ready assembly of :theconnection. Thus, vertical movement 10f the valve stem :21! maises rand iowers the core :24, which marries the segments :23 along :as ea unit :because of the Slip and groove connection therebetween, there- ."by opening :or fclosing the valve. 'fl he :stem ions provided with .an annular shoulder or stop d6 having a conical portion which abuts against a :conical seat in an @upper portion of the wall of the chamber This shoulder :serves to limit the upward travel :of the gate andialso "to prop- -erly align the gate ports Z5 and 126 with the housing zports Hand 13 :in :open position of The lower. end of the more 24 abut the closure plate if! and thereby limitthe downward travel 50f the gate np'on 'movement iOf the valve into closed position.

JQperation of the valve is evident from the :above description. Assuming the valve :in the :open rand sealed position shown figures .1 :and 3,:and it is desired to close the valve. Tina :handle 39 first is turned to contract the agate rand unseal the valve, as shown in Figure JThe handwheel 2:! then .is operated to move "the .gate into closed position, :shown .in Figure .2, whereupon the .gate is expanded and the valve rresealed ,by the operation of the handle 53-9.

Some of the basic .features of the present in- 'vention may be retained "in a gate construction having :only itWO sections, :as shown .Figure '6. In this modification, one section 4:! is laterally 'displaceable rand :eorresponds to :an integration of the core 324 and one "of the segments .213 :of the previously described ithreesection gate. fiBhe other :section is like a segment 23 of a, three section :gate. Hence, the laterally displaceable section 4:! has one wedging .face 29 and wne sealing .face 21. To .zpermit lateral movement of this :section -41, the lateral iguides J15, adjacent the valve seat 14 corresponding to the sealing .iace 32'! of the section, :are omitted. The operation of the two section gate structure is otherwise the same as that of the three section construction. Since 'an undesirable loaded iwiping acion "occurs, however, between the sealing :faces of the laterally rdisplaceable section 4?! and its :cor-

, responding valve seat 1| 4, this simplified structure finds its primary usefulness in :a valve which is designed to handle pressure on one :side only.

The invention has been shown :as :appiied to :a valve :of the rising stein type, :i. e. onesin which the :stem .20 is threaded to :a handwheiel 22! "and :fixed against :rotation :in the :gate. invention :may

.be incorporated, however, :in a "valve or" the non rising stem type, i. 4;. :one in which the stem 'is threaded into "the :gate and ffixed .to fa :handwlheel to rotate therewith. In iboth typesofvalves, some relative lateral movement between the-valve stem :and the :core 24., or laterall displaceable section 4:1, enustlbe permitted. .Sin'cesuch relative move- ;.ment is wery :s'ligh't, it may be provided for :a valve of the non-rising stem type by looseness in the threaded connection 'between the stem the core. IProvis'ion ior th-is relative lateral moveimentzaiso may be made by the-construction shown i11.Figures Tar-1d 8. 'lnfitl iis construction, the'c'ore 1-24 is =provided'with'a threaded bushing i8 "which fits with "lateral looseness in the core slot :35 in 'muchfithe-same'manner'as the'hea'dit on the stein of a rising stem type valve. The'bushing 38 has a head i9 to engage the under side of the overhanging portions of the undercut slot "i5 and an annular enlargement to engage the "top of "the core. The valve-stem this threaded through the bushing and extends 'therebeiow -(in the open .pO- sition of the 'valve) into a stem-receiving cavity,

1 in the core body which iorms an extension of the slot 45. The operation of this type of valve is the same as that of the rising-stem type.

It will be seen that this invention'provides a greatly improved gate valve. The valve is readily operable in spite of pressure lock, and will handle pressure fiuids from either side. Abrasive wear of the sealing surfaces is reduced to the minimum, thus permitting a wider choice of materials for such surfaces. Positive contraction of the gate is accomplished without th use of springs. The clearance between the sealing surfaces of the'valve is "controlled and adjustable in both fully open and fully closed positions. The valve is highly effective for use under adverse service conditions without leakage. Structural changes, however, which retain the basic features of the invention will be evident to one skilled in the art. Accordingly, the invention embraces all embodiments that come within the scope and spirit of the following claims.

I claim:

1. A gate valve comprising: a housing having aligned ports provided with opposed parallel valve seats; a sectional gate mounted for endwise rectilinear movement between said seats to open and close the valve, said gate including at least two abutting members, one of which has an outer face parallel to one of said seats for sealing engagement therewith and the other of which is displaceable laterally of said seats normal to the endwise movement of said gate and disposed between said one member and the other of aid seats, the abutting faces of said members being parallel and inclined with respect to said seats to provide wedging surfaces effective to expand said gate normally of said seats and force said one member into sealing engagement with said one seat upon lateral displacement of said other member in one direction; guide means for maintaining said one member against displacement laterally of said seats normal to the movement of said gate; means connecting said members for simultaneous endwise movement; stem means for moving said gate endwise to open and close the valve; and means operable independently of said stem means for laterally displacing said other member.

2. A gate valve comprising: a housing having aligned ports provided with opposed parallel valve seats; a sectional gate mounted for endwise rectilinear movement between said seats to open and close the valve, said gate including at least two abutting members, one of which has an outer face parallel to one of said seats for sealing engagement therewith and the other of which is displaceable laterally of said seats normal to the endwise movement of said gate and disposed between said one member and the other of said seats, the abutting faces of said member being parallel and inclined with respect to said seats to provide wedging surfaces efiective to expand said gate normally or said seats and force said one member into sealing engagement with said one seat upon lateral displacement of said other member in one direction; guide means for maintaining said one member against displacement laterall of said seats normal to the movement of said gate; interfitted means extending parallel to said abutting faces and connecting said members for relative lateral displacement therebetween and for simultaneous endwise movement, said means providing wedging surfaces effective to contract said gate normally of said seats upon lateral displacement of said other member in the other direction; stem means for moving said gate endwise to open and close the valve; and means operable independently of said stem means for laterally displacing said other member.

3. A gate valve comprising: a housing having aligned ports provided with opposed parallel valve seats; a sectional gate mounted for endwise rectilinear movement between said seats to open and close the valve, said gate including two members each having a face parallel to a corresponding valve seat for sealing engagement therewith and wedge means interposed. between said members for lateral displacement normal to the endwise movement of said gate, lateral displacement of said wedge means in one direction being efiective to expand said gate normally of said seats and forcefully seat said members oppositely against their respective seats; guide means for maintaining said members against displacement laterally of said seats normal to the movement of said gate; means connecting said wedge means and said members for simultaneous endwise movement; stem means for moving said gate endwise to open and close the valve; and means operable independently of said stem mean for laterally displacing said wedge means.

4. A gate valve comprising: a housing having aligned ports provided with opposed parallel valve seats; a sectional gate mounted for endwise rectilinear movement between said seats to open and close the valve, said gate including two members each having a face parallel to a corresponding valve seat for sealing engagement therewith and wedge means interposed between said members for lateral displacement normal to the endwise movement of said gate, lateral displacement of said wedge means in one direction being effective to expand said gate normally of said seats and forcefully seat said members oppositely against their respective seats; guide means for maintaining said members against displacement laterally of said seats normal to the movement of said gate; interfitted means connecting each member to said wedge means for relative lateral displacement therebetween and for imultaneous endwise movement, said means providing wedging surfaces effective to contract the gate normally of said valve seats and forcefully unseat at least one of said members from its corresponding valve seat upon lateral displacement of said wedge means in the other direction; stem means for moving said gate endwise to open and close the valve; and means operable independently of said stem means for laterally displacing said wedge means.

5. A gate valve comprising: a housing having aligned ports provided with opposed parallel valve seats; a sectional gate mounted for endwise rectilinear movement between said seats to open and close the valve, said gate including two segments each having a face parallel to a corresponding valve seat for sealing engagement therewith and a core interposed'between said segments for displacement laterally of said seats normal to the endwise movement-of said gate, each set of abutting faces of said segments and said core being parallel and the two sets of said abutting faces being laterally divergent to provide two sets of wedging surfaces effective to expand said gate normally of said seats and forcefully seat said segments oppositely against their respective valve seats upon lateral displacement laterally of said seats normal to the movement of said gate of said core in one direction; guide means for maintaining said segments against lateral displacement; means connecting each of said segments to said core for simultaneous endwise movement;

end stem means connected to said core for moving said core and thereby said segments endwise to open and close the valve, the connection between said end stem and said core permitting relative lateral movement therebetween; and lateral stem means connected to said core for laterally displacing said core, the connection between said lateral stem and said core permitting relative movement therebetween parallel to the movement of said gate.

6. The structure defined by claim in which the core has an undercut slot opening to one side in one end thereof and the end stem means has a head fitting with lateral clearance in said slot to permit said relative movement between said core and said end stem means.

7. The structure defined by claim 5 in which the core has a gI'OOVe in a lateral edge thereof extending parallel to the movement of the gate, end portions of said groove being undercut, and the lateral stem means has a head fitting said groove to permit said relative movement between said core and said lateral stem means.

8. The structure defined by claim 5 in which the core and each segment are interconnected adjacent both ends thereof by a transversel interlocking rib and groove, each said rib and groove extending normal to the movement of the gate and parallel to the corresponding set of abutting faces, whereby lateral displacement of said core in the other direction is effective to contract the gate normally of the valve seats and forcefully unseat at least one of said segments from its corresponding valve seat.

9. A gate valve comprising: a housing having aligned ports provided with opposed parallel valve seats; a sectional gate mounted for endwise rectilinear movement between said seats to open and close the valve, said gate including a pair of ported segments having parallel outer sealing faces to engage said seats and laterally divergent inner faces and a ported core interposed between said segments for lateral displacement normal to the endwise movement of said gate, the segment ports and the core port being adapted to be aligned with said housing ports in the open position of the valve to permit unobstructed flow therethrough, said core having laterally divergent faces parallel to said segment inner faces to provide two sets of wedging surfaces efiective to expand said gate normally of said seats and force said segments oppositely into sealing engagement with said seats upon lateral displacement of said core in one direction; guide means adjacent each of said seats for maintaining said segments against displacement laterally of said seats normal to the movement of said gate; means connecting each of said segments to said core for simultaneous endwise movement; stem means connected to one end of said core for moving said gate endwise to open and close the valve; and second stem means connected to a lateral edge of said core for laterally displacing said core.

10. A gate valve comprising: a housing having aligned ports provided with opposed parallel valve seats; a sectional gate mounted for endwise rectilinear movement between said seats to open and close the valve, said gate including two abutting members having parallel outer sealing faces to engage said seats and parallel opposed inner faces inclined with respect to said seats to provide wedging surfaces effective to expand said gate normally of said seats and forcefully seat said members oppositel against their respective valve seats upon relative displacement between said members in one direction laterally of said seats normal to the endwise movement of said gate; guide means for maintaining one of said members against lateral displacement, said other member being laterally displaceable; means con necting said members for simultaneous endwise movement; stem means for moving said gate endwise to open and close the valve; and means operable independently of said stem means for laterally displacing said other member.

11. The structure defined by claim 10 including interfitted means connecting the members for relative lateral displacement, said connection being effective to contract the gate normally of the valve seats and forcefully unseat at least one of said members from its corresponding valve seat upon lateral displacement of said other member in the other direction. 7

MILTON PAUL LAURENT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,134,811 Berger Apr. 6, 1915 1,250,041 Synder 1 Dec. 11, 1917 2,344,747 Sperry Mar. 21, 1944 FOREIGN PATENTS Number Country Date 56,160 Germany of 1891 148,036 Austria Dec. 10, 1936 Certificate of Correction Patent No. 2,537,470 January 9, 1951 MILTON PAUL LAURENT It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 4, line 47, for dislacement read displacement; column 6, line 42, for acion read action; column 8, lines 7 O and 71, strike out laterally of said seats normal to the movement of said gate and insert the same in line 7 4, after the syllable ment and before the semicolon; line 73, strike out the word lateral; and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 6th day of March, A. D. 1951.

[sun] THOMAS F. MURPHY,

Assistant C'ommz'ssz'oner of Patents. 

